linux_dsm_epyc7002/Documentation/virtual/kvm/devices/vm.txt

Generic vm interface
====================================

The virtual machine "device" also accepts the ioctls KVM_SET_DEVICE_ATTR,
KVM_GET_DEVICE_ATTR, and KVM_HAS_DEVICE_ATTR. The interface uses the same
struct kvm_device_attr as other devices, but targets VM-wide settings
and controls.

The groups and attributes per virtual machine, if any, are architecture
specific.

1. GROUP: KVM_S390_VM_MEM_CTRL
Architectures: s390

1.1. ATTRIBUTE: KVM_S390_VM_MEM_ENABLE_CMMA
Parameters: none
Returns: -EBUSY if a vcpu is already defined, otherwise 0

Enables Collaborative Memory Management Assist (CMMA) for the virtual machine.

1.2. ATTRIBUTE: KVM_S390_VM_MEM_CLR_CMMA
Parameters: none
Returns: 0

Clear the CMMA status for all guest pages, so any pages the guest marked
as unused are again used any may not be reclaimed by the host.

1.3. ATTRIBUTE KVM_S390_VM_MEM_LIMIT_SIZE
Parameters: in attr->addr the address for the new limit of guest memory
Returns: -EFAULT if the given address is not accessible
         -EINVAL if the virtual machine is of type UCONTROL
         -E2BIG if the given guest memory is to big for that machine
         -EBUSY if a vcpu is already defined
         -ENOMEM if not enough memory is available for a new shadow guest mapping
          0 otherwise

Allows userspace to query the actual limit and set a new limit for
the maximum guest memory size. The limit will be rounded up to
2048 MB, 4096 GB, 8192 TB respectively, as this limit is governed by
the number of page table levels. In the case that there is no limit we will set
the limit to KVM_S390_NO_MEM_LIMIT (U64_MAX).

2. GROUP: KVM_S390_VM_CPU_MODEL
Architectures: s390

2.1. ATTRIBUTE: KVM_S390_VM_CPU_MACHINE (r/o)

Allows user space to retrieve machine and kvm specific cpu related information:

struct kvm_s390_vm_cpu_machine {
       __u64 cpuid;           # CPUID of host
       __u32 ibc;             # IBC level range offered by host
       __u8  pad[4];
       __u64 fac_mask[256];   # set of cpu facilities enabled by KVM
       __u64 fac_list[256];   # set of cpu facilities offered by host
}

Parameters: address of buffer to store the machine related cpu data
            of type struct kvm_s390_vm_cpu_machine*
Returns:    -EFAULT if the given address is not accessible from kernel space
	    -ENOMEM if not enough memory is available to process the ioctl
	    0 in case of success

2.2. ATTRIBUTE: KVM_S390_VM_CPU_PROCESSOR (r/w)

Allows user space to retrieve or request to change cpu related information for a vcpu:

struct kvm_s390_vm_cpu_processor {
       __u64 cpuid;           # CPUID currently (to be) used by this vcpu
       __u16 ibc;             # IBC level currently (to be) used by this vcpu
       __u8  pad[6];
       __u64 fac_list[256];   # set of cpu facilities currently (to be) used
                              # by this vcpu
}

KVM does not enforce or limit the cpu model data in any form. Take the information
retrieved by means of KVM_S390_VM_CPU_MACHINE as hint for reasonable configuration
setups. Instruction interceptions triggered by additionally set facility bits that
are not handled by KVM need to by imlemented in the VM driver code.

Parameters: address of buffer to store/set the processor related cpu
	    data of type struct kvm_s390_vm_cpu_processor*.
Returns:    -EBUSY in case 1 or more vcpus are already activated (only in write case)
	    -EFAULT if the given address is not accessible from kernel space
	    -ENOMEM if not enough memory is available to process the ioctl
	    0 in case of success